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 A handful of odd CPUs in DIP 
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Joined: Wed Jan 09, 2013 6:54 pm
Posts: 1647
Seen on a blog, two small collections of odd CPUs under consideration for building a calculator with (for fun) ... s.html?m=1 ... s.html?m=1

HD6120 - This is a PDP-8 on a chip, which has a 12 bit architecture. One homebrew project I have seen uses it. I'm mainly curious about it because the assembly instructions for it are so bizarre. Like the 1802, I am interested in it because it is quirky, not because it has much processing power.

L3903-57 - This is part of an offshoot of the 6502 family that was used as part of modem chipsets. It has a lot of microntroller features like internal RAM and peripherals like timers. It runs at up to 20.5MHz, compared to the 8MHz of the 6502 derived microcontroller made by WDC and the 14MHz of a 65C02. It is not entirely compatible with the 65C02 since it handles indirect jump instructions differently and has additional instructions for threaded code. It might have more flexible timing constraints, which could be helpful even if it isn't running at top speed.

N8X305N - This is the weirdest processor in the list by far. It has a 16-bit wide instruction bus but no dedicated bus for data. External data access can only be conducted through two "ports." The really strange thing about this chip is that it only has eight instructions. The OR instruction, for example, has to be synthesized from AND and XOR. It seems like it would be a big challenge to write assembly for this.

SAB80199 - This is a neat 16-bit chip made by Siemens. Unfortunately, I can't find a datasheet for it, so I'm not sure yet if it would work well for a calculator.

TMS9995 - This is another older but interesting architecture. It has some neat features, considering how old it is, like a relocatable register file in RAM, 16 bit ALU, and many addressing modes. The data bus is 8 bit, unlike its predecessor the TMS9900, but it only requires one 5v source, rather than three different voltages. It has a built in shift register, which I might be able to use for memory mapping. From what I can tell, the low clock speed, many cycles per instruction, and 8 bit bus mean performance probably won't be very high. If I ever use this, it would be out of curiosity for the architecture.

TMS99105 - This is a superset of the TMS9995 with new instructions including stack operations. The most interesting thing is the macrostore feature where you can remap unused opcodes. I'm not sure how this is much better than a subroutine call, other than saving a tiny amount of program memory, but it does allow you to address an extra 64k of memory space. Like the TMS9995, it comes in a DIP package, but instead of a separate address bus with a multiplexed 8 bit data bus, it multiplexes a 16 bit data bus and a 16 bit address bus on the same pins. It's clock speed is twice as fast as the TMS9995. The one downside I have found is that it costs about $35 on eBay, compared to only about $5 for the TMS9995.

In partial conclusion:
This list ended up a lot longer than I intended because I found so many new chips. Here are my top picks from the list:
    LPC1114 - My first priority is to finish the Pocket Calculator I recently started using this chip.
    DS89C450 - The next calculator I am planning on building will use this chip, since I should be able to avoid using a CPLD, and it may be faster than the 6502 calculator I want to build.
    65C02 - I have wanted to use this chip for a long time, but I want to try out some of my ideas building other calculators and work on a program I have been thinking about for preprocessing 6502 assembly.
    6309 and 1805 - Neither of these chips is especially powerful, but it would be fun to make a simpler calculator with one of them.
    XA series and NS32CG160 - I would also like to make a calculator out of one of the more powerful processors in PLCC package and these two look like the best candidates.

Tue Nov 05, 2019 2:20 pm

Joined: Mon Oct 07, 2019 2:41 am
Posts: 273
Any chip used, will be alot simpler than the old way.
A TTL calculator can be found here, now in PDF form from 1873 ... well almost. ... /digi-cal/

Tue Nov 05, 2019 11:15 pm

Joined: Wed Jan 09, 2013 6:54 pm
Posts: 1647
Nice find! The Digi-Cal project by R. W. Coles
At last - a high speed desk top calculator for constructors. It adds, subtracts, multiplies, divides, automatically squares and operates with stored constant.
about which we read this:
a long-running DIY desktop digital calculator – the PE Digi-Cal (July 1972 onwards) was built with TTL logic and took no less than eleven monthly articles to complete. Unfortunately, it was obsolete almost before constructors turned off their soldering irons because single-chip calculators came onto the market around that time

It seems to have 8 digits, although multiplication uses 10, and only 6 digits can be entered. The 7 segment filament-based display uses a 20V supply - yikes! The kit of parts costs £110 - a huge amount at that time, maybe £1400 equivalent. It's all small scale integration - no ALU chips here. (edit: and a diode rom for the micro sequencing.)

There's another version of the same PDF scan on the Internet Archive: ... 73_8879126

Wed Nov 06, 2019 9:24 am
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